Proposal: Strict scanl, scanl1 and mapAccumL

[Bas van Dijk]

Hi,

Data.List exports strict versions of foldl an foldl1. I think it
should also export these strict versions of scanl, scanl1 and
mapAccumL:

scanl' :: (a -> b -> a) -> a -> [b] -> [a]
scanl' f q ls =  q : (case ls of
                        []   -> []
                        x:xs -> let q' = f q x
                                in q' `seq` scanl f q' xs)

scanl1' :: (a -> a -> a) -> [a] -> [a]
scanl1' f (x:xs) =  scanl' f x xs
scanl1' _ []     =  []

mapAccumL' :: (acc -> x -> (acc, y)) -> acc -> [x] -> (acc, [y])
mapAccumL' _ s []     =  (s, [])
mapAccumL' f s (x:xs) =  (s'',y:ys)
    where
      (s', y ) = f s x
      (s'',ys) = s' `seq` mapAccumL' f s' xs

Is there a good reason they're not included?

Discussion deadline: 2 weeks (till Monday 26 November).

Regards,

Bas